Abstract A075: Establishing the interaction mechanism of oncoprotein, Mucin1, and extracellular vesicle marker protein, Alix, in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains an aggressive disease with devastating mortality rates largely due to a poor understanding of its progression mechanism. Small extracellular vesicles (sEVs) are used by cancer cells to aid in their progression, and tumor-derived EVs (TEVs) show a distinct protein cargo composition potentially contributing to this rapid progression and metastasis of PDAC. To investigate this phenomenon, we isolated sEVs from conditioned media of pancreatic cancer cell lines using ultracentrifugation and characterized them by transmission electron microscopy (TEM), nanoparticle tracking analysis, and immunoblotting. These sEVs were then used in several studies to investigate critical TEV cargo sorting machinery. For instance, PDAC-derived sEVs have selective enrichment of the oncogenic transmembrane protein Mucin1 (MUC1). Preliminary MUC1KO studies from our lab revealed that MUC1 potentially regulates sEV formation, where we saw a clear impact on sEV cargo in the absence of MUC1. Additional studies found that the cytoplasmic adaptor protein ALG-2-Interacting Protein X (Alix), a protein known to play a critical role during TEV formation, regulates MUC1’s presence in sEVs. From this discovery, we then identified a novel MUC1-Alix interaction, which was confirmed using several techniques, including co-immunoprecipitation (CoIP). To define the Alix-interacting domain of MUC1, we utilized in silico modeling and localized surface plasmon resonance (LSPR) of MUC1.CT and Alix to quantify the interaction. This revealed the cytoplasmic tail of MUC1 (MUC1.CT) as the Alix-interacting domain. Moving forward, our central hypothesis for this study is that this MUC1.CT-Alix interaction utilizes a conserved binding motif that targets Alix to the endosomal membrane and contributes to the formation of MUC1+ sEVs. While a distinct sEV biogenesis pathway employed by cancer cells has not yet been defined, our studies will provide insight into the potential sEV sorting mechanism of MUC1 and other cancer biomarkers and advance the understanding of PDAC progression. Citation Format: Kristine V Hoagstrom, Ying Huang, Gloria E Borgstahl, Michael A Hollingsworth. Establishing the interaction mechanism of oncoprotein, Mucin1, and extracellular vesicle marker protein, Alix, in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A075.